IEEE (Institute of Electrical and Electronics Engineers) 802.11u is a supplementary standard stipulated for IEEE 802.11. The main research content of the IEEE 802.11u standard is a function of a WLAN (Wireless Local Area Network) interworking with an external network. The function allows a STA (station) to obtain service access of the external network. The external network is an external network that is subscribed to or has other features. For example, the STA may obtain a subscription service provided by a subscription service provider network (SSPN).
An interworking element is newly added to the IEEE 802.11u standard to serve as a carrier of capabilities and information of interworking between an AP (access point) and the STA, so as to implement interworking between a WLAN infrastructure network and an external network. In addition, a roaming consortium information element is also newly added to the IEEE 802.11u standard to indicate identification information of a related subscription service provider (SSP), and the AP transmits the element, which helps to quickly start authentication of security credentials. Specifically, the AP sends a beacon and a probe response that contain the interworking element and the roaming consortium information element to assist the STA in network selection.
If the interworking element appears in the beacon and the probe response, it indicates that the STA supports the GAS (Generic Advertisement Services) protocol. GAS can facilitate the network selection of the STA. No matter whether the STA is in an associated state or in a non-associated state, GAS can provide a transmission mechanism for advertisement services, to implement a network discovery and selection function. A query request STA and a query response AP implement a GAS query through an interaction frame. Specifically, in a synchronous query state, first, the query request STA sends a GAS initial request frame to the query response AP and requires the query response AP to feedback expected query information; after receiving the request, the query response AP uploads the query request information to an advertisement server and requires the advertisement server to feedback corresponding query information; the advertisement server feeds back the corresponding query information; and finally, the query response AP feeds back the fed back query information to the query request STA by using a single GAS initial response frame or one or more GAS recovery response frames as a carrier. Which carrier is adopted is related to the size of the query information. If the length of the query information is too long, the query information is fragmented, and after receiving the GAS initial response frame, the query request STA may continue to send a GAS recovery request frame to request obtaining of subsequent fragments. In an asynchronous query state, first, the query request STA sends a GAS initial request frame to the query response AP and requires the query response AP to feed back expected query information; after receiving the request, the query response AP uploads the query request information to the advertisement server and requires the advertisement server to feed back corresponding query information; then, the query response AP sends a GAS initial response frame which does not contain the query information to the query request STA and instructs the query request STA to get the query information after a period of time; the advertisement server feeds back the corresponding query information; after the time designated by the AP, the query request STA returns the query information to the AP through a recovery request frame; and finally, the query response AP feeds back the fed back query information to the query request STA by using a single GAS recovery response frame or one or more GAS recovery response frames as a carrier. Which carrier is adopted is related to the size of the query information. If the length of the query information is too long, the query information is fragmented, and after receiving the GAS recovery response frame, the query request STA may continue to send a GAS recovery request frame to request obtaining of subsequent fragments.
In an existing 802.11u mechanism, assuming a STA obtains, through a GAS query process, information of an external network supported by AP1 and is successfully associated with AP1, then, the STA is disassociated from AP1 for a certain reason (for example, the STA is taken to an area covered by AP2 and is associated with the new AP2 for communication, or the STA actively switches to a non-WLAN network for communication without departing from the coverage of AP1), and the STA needs to re-establish the association with AP1 for a certain reason (for example, the STA is taken back to the area covered by AP1, or the STA actively switches back to the WLAN network for communication without departing from the coverage of AP1) after a period of time, the STA needs to re-obtain, through the GAS query process, the information of the external network supported by AP1, so as to become associated with AP1 again.
It can be seen that, in the existing 802.11u mechanism, even if the information of the external networks remains the same all the time, every time the STA establishes the association with AP1, the STA needs to re-obtain, through the GAS query process, the information of the external network supported by the AP1. This process has a low efficiency, and is time-consuming and power-consuming, thereby affecting user experience of the STA.